/*
	       File: RSAEncryption.cs
	Create Date: 2007-09-11
	    Version:

	Description:


	 Change log:


*/
using System;
using System.Collections.Generic;
using System.Text;

namespace GuerillaProgrammer.FileProcessor.Encryption
{
    public class RSAEncryption
    {
        #region Private member fields
        #endregion

        #region Constructors and cleanup methods
        public RSAEncryption()
        {
        }
        #endregion

        #region Private implementation methods
        #endregion

        #region Class properties
        #endregion

        #region Events handlers
        #endregion

        #region Public interface
        public string EncryptString(string inputString, int dwKeySize, string xmlString)
        {
            RSACryptoServiceProvider rsaCryptoServiceProvider = new RSACryptoServiceProvider(dwKeySize);
            rsaCryptoServiceProvider.FromXmlString(xmlString);
            int keySize = dwKeySize / 8;
            byte[] bytes = Encoding.UTF32.GetBytes(inputString);
            // The hash function in use by the .NET RSACryptoServiceProvider here 
            // is SHA1
            // int maxLength = ( keySize ) - 2 - 
            //              ( 2 * SHA1.Create().ComputeHash( rawBytes ).Length );
            int maxLength = keySize - 42;
            int dataLength = bytes.Length;
            int iterations = dataLength / maxLength;
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0; i <= iterations; i++)
            {
                byte[] tempBytes = new byte[(dataLength - maxLength * i > maxLength) ? maxLength : dataLength - maxLength * i];
                Buffer.BlockCopy(bytes, maxLength * i, tempBytes, 0, tempBytes.Length);
                byte[] encryptedBytes = rsaCryptoServiceProvider.Encrypt(tempBytes,true);
                // Be aware the RSACryptoServiceProvider reverses the order of 
                // encrypted bytes. It does this after encryption and before 
                // decryption. If you do not require compatibility with Microsoft 
                // Cryptographic API (CAPI) and/or other vendors. Comment out the 
                // next line and the corresponding one in the DecryptString function.
                Array.Reverse(encryptedBytes);
                // Why convert to base 64?
                // Because it is the largest power-of-two base printable using only 
                // ASCII characters
                stringBuilder.Append(Convert.ToBase64String(encryptedBytes));
            }
            return stringBuilder.ToString();
        }
        public string DecryptString(string inputString, int dwKeySize, string xmlString)
        {
            RSACryptoServiceProvider rsaCryptoServiceProvider = new RSACryptoServiceProvider(dwKeySize);
            rsaCryptoServiceProvider.FromXmlString(xmlString);
            int base64BlockSize = ((dwKeySize / 8) % 3 != 0) ? (((dwKeySize / 8) / 3) * 4) + 4 : ((dwKeySize / 8) / 3) * 4;
            int iterations = inputString.Length / base64BlockSize;
            ArrayList arrayList = new ArrayList();
            for (int i = 0; i < iterations; i++)
            {
                byte[] encryptedBytes = Convert.FromBase64String(inputString.Substring(base64BlockSize * i, base64BlockSize));
                // Be aware the RSACryptoServiceProvider reverses the order of 
                // encrypted bytes after encryption and before decryption.
                // If you do not require compatibility with Microsoft Cryptographic 
                // API (CAPI) and/or other vendors.
                // Comment out the next line and the corresponding one in the 
                // EncryptString function.
                Array.Reverse(encryptedBytes);
                arrayList.AddRange(rsaCryptoServiceProvider.Decrypt(encryptedBytes, true));
            }
            return Encoding.UTF32.GetString(arrayList.ToArray(Type.GetType("System.Byte")) as byte[]);
        }
        #endregion
    }
}
